Visualize electronmicroscopically the 3 feet terminus of S28 rRNA by polyadenylation via polynucleotide phosphorylase (PNPase) and poly-5BUdR hybridization. 3 feet end identification by affinity coupling of RNA and PNPase and subsequent crosslinking via glutaraldehyde. Short-track polyadenylation (n equals 20-30) of rRNA by PNPase, controlled hydrolysis (approx. 1cut/S28), retention of polyadenylated "halves" of S28 on poly dT-cellulose columns and secondary structure electronmicroscopy of the "flow through halves", i.e., the 5 feet termini of S28, and the retained halves, i.e., 3 feet termini. Probing transcriptional organization of HnRNA by UV truncation of transcripts. Study in vivo polyadenylation of truncated RNA and stability and transport of UV truncated RNA to the cytoplasm.